Devices for preventing unauthorized use of video-cassettes

ABSTRACT

A conventional video cassette comprises a tape transport mechanism (1) comprising two reels each with an internally splined tape drive hole, contained in a protective housing (2). The protective housing (2) of the cassette is provided with two circular access holes through which the tape drive holes of the reels can be accessed, and normally the reels themselves are pressed into firm contact with the underside of the cassette protective housing (2) by a leaf spring (3). The device (10) of the invention can be inserted into either of the internally splined tape drive holes and pushed downwardly with compression of the associated leaf spring (3) of the video cassette until the underside of the protective housing (2) is exposed. Thereafter detent members (15) engage beneath the protective housing (2), and the device can be removed from the tape drive hole only by an authorized person using a key (17).

DESCRIPTION

1. Field of Invention

The invention is in the field of video-cassettes to try and ensure useof a video-cassette by an authorised person only.

2. Background

Various devices have been proposed for preventing the unauthorisedplaying of video tapes on a video cassette recorder/playback unit. Someproposals have sought to inactivate the recorder/playback unit, as withU.S. Pat. No. 4,527,405 (Renick) which relates to a dummy cassette thatcan be locked into the tape loading opening of the recorder/playbackunit, this inactivating the unit. Disadvantages of this solution arethat the use of the recorder/playback unit is prevented for allrecordings, not merely for selected recordings which are intended tohave a limited audience; and that loss of the key when the dummycassette is locked in position can render the recorder/playback unitunusable. It will be appreciated that this is a significantly moreonerous penaly than simply the inability to load and use one specificcassette.

A more relevant solution is one that inactivates individual cassettes,thus enabling a parent, for example, to impose a degree of censorshipand prevent young members of a family from viewing material thought tobe unsuitable. Devices have been proposed which prevent removal of thevideo cassettes from their storage or library cases. Such devicesprovide a very low level of security, however, as the library case caneasily be forced open without damage to the cassette. If such forcingdamages or destroys only the library case, then that is no deterrent tothe potential unauthorised user, as the tape transport mechanism in itsprotective housing is likely to be undamaged.

Recent proposals have been directed to the provision of security meansassociated with the tape cassette itself. British Patent Application No.2,138,778 A (Dunne) proposes the use of a bung which is a friction-fitin the splined holes of the tape reels of the tape transport mechanism.If a cassette fitted with such a bung were loaded into a video cassetterecorder/playback unit, then sensors provided on the unit would fail torecognize the necessary pair of splined drive holes and a cassetteejection mechanism would be activated. Such sensors and ejectionmechanism are provided on all video recorders to check against themistaken loading of the cassette upside-down. The most significantdisadvantage of the Dunne proposal is that because the bung is simply afriction fit it can easily be removed using a pointed instrument withoutdamage to the cassette, so that the level of security is extremely low.

A slightly higher level of security is inherent in the propsal of FrenchPatent Application No. 2,545,305 A (Drahi) which proposes the insertionof a key-lockable member into the optical sensor access hole of a videocassette. A standard cassette comprises a circular recess in itsunderside, having a diameter of 12 mm. When the cassette is lowered intoa video recording/playback unit, an optical sensor of the video unit isreceived in this recess, and through lateral openings in the wall of thecircular recess senses whether a video tape is present in the cassette.The optical sensor is designed to distinguish between the presence andabsence of opaque video tape within the cassette, so as to stop therecording/playback unit either when the transport leader or trailer tapeis reached or when there is a brake in the tape. It is not, however,designed to sense whether or not the circular recess is provided in thecassette. Therefore when this recess is blocked with a plug insert, asin Drahi, and the cassette is loaded into a video recorder/playbackunit, the cassette handling mechanism of the unit pushes the plug insertdown onto the optical sensor, thus placing a strain on the opticalsensor of the video recorder/playback unit which it is not designed toresist. This can seriously damage that sensor.

Drahi specifically teaches that, of the recesses available in a videocassette, it is preferred to design the plug insert to fit the opticalsensor recess. This recess is provided with lateral passages which formshoulders beneath which the locking bolt can engage. None of the otherrecesses in a conventional video cassette have such lateral passages,although there are others which have similar internal shoulders beneaththe surface of the cassette. Also the optical sensor recess straddles acooperating non-circular shallow groove in the cassette case so that arotary key can be used to lock and release the plug insert, obtainingits reaction or purchase from a nose of the plug insert received in thegroove. Also the optical sensor recess is the largest diameter recess inthe cassette case to have such internal shoulders and a cooperatinggroove. Even so, the maximum diameter of any plug insert made accordingto the teachings of Drahi is 12 mm, being the diameter of the opticalsensor recess in a standard cassette. This is barely sufficient to housea reliable lock mechanism. Drahi therefore proposes a bolt which isoptionally spring-biassed to the retracted position and which requiresthe use of a key both to advance and to retract the bolt. It followsthat the lock mechanism disclosed in Drahi, even in the preferredembodiment illustrated, is one that could be released very easily usinga pin, wire or pointed instrument to rotate the barrel either assistedby the bias of the spring or, if the optional spring is omitted, withoutany counter-bias.

There therefore remains a need for a device for preventing theunauthorized use of a video cassette which provides a high degree ofsecurity, which cannot be removed or inactivated using normallyavailable household implements, and which does not cause damage to thevideo recorder/playback unit. The present invention provides such adevice, making use of features of conventional video tape cassetteswhich were not appreciated by Dunne or Drahi. The invention is believedto be original first in its use of those features of a conventionalcassette, as detailed below; secondly in the general method used forproviding enhanced security using simple devices; and thirdly in theingenious mechanisms of the device which ensure reliable operation andsufficient security have regard to the purpose of the invention.

SUMMARY OF THE INVENTION

The invention thus provides a device for preventing unauthorised use ofa video-cassette by blanking off the internally splined tape drive holeof a tape transport reel of the video-cassette to prevent unauthoriseduse of the cassette, CHARACTERISED IN THAT a blanking body shaped to fitthe tape drive hole is provided with at least one detent mounted to passbetween the tape transport reel of the cassette and the underside of aprotective housing of the cassette on compression of the spooltensioning spring by the tape transport reel; and key-release means foreffecting retraction of the detent or detents to permit removal of theblanking body. The device can be unobstrusively inserted inside a tapedrive hole of a video cassette, and lock in position without adding tothe overall bulk of the cassette or interfering with its storage in alibrary case. Upon insertion of the cassette into the videorecorder/playback unit with the device in position, the videorecorder/playback unit will reject the cassette using its existingsafety mechanisms which detect the accessibility of the two tape driveholes in the video cassette. When a cassette protected by a deviceaccording to the invention is rejected by a video recorder/playback unitthere is no strain on any of the parts of the unit, as the existingsafety mechanism are designed specifically to sense the presence andaccessibility of the two drive holes, so that at no stage is thecassette lowered forcefully against any fragile or sensitive parts ofthe unit. No modification of the cassette, cassette library case orvideo unit is thus required and the device can be sold in shops as anaccessory for both BETAMAX (Trade Mark) and VHS (Trade Mark) type videocassettes.

It is not apparent from a visual inspection of a video tape cassette howthe device of the invention is able to lock so positively into the tapedrive holes. The hole into which the device is inserted has no visibleshoulder beneath which a detent can engage. The bung of Dunne was simplya friction fit. However the Applicants have made use of the fact thatthe reels of the tape transport mechanism of a standard cassette arespring-mounted. A spool tensioning spring beneath each reel biases itinto close contact with the opposite wall of the protective housing.Depression of this spring permits sufficient movement of the reel,without damage to the tape transport mechanism, to allow the one or moredetents of the device to pass between the depressed reel and theunderside of the protective housing, to allow a secure and positivelocking of the device to the protective housing.

Advantageously this engagement of the detent or detents with theunderside the protective housing is permitted only when there is fullcompression of the spool tensioning spring, so that the device cannot bedepressed further into the tape drive hole after locking has beenachieved. The or each detent is preferably biased radially outwardlyinto its locking position by resilient means incorporated into thedevice. The taper which is conventionally moulded into the cassetteprotective housing around the tape drive holes as a centering aid isadvantageously used as a cam surface to cam the detent or detentsradially inwardly against the bias of the resilient means as the deviceis pushed axially down into the tape drive hole. On the underside of theprotective housing, the detent or detents spring out under the bias ofthe resilient means to lock the device in position. By making the detentor detents sufficiently strong, the device cannot be removed without akey except by breaking the protective housing or dismantling the entirecassette.

Advantageously one or more pairs of detents are provided, the detents ofeach pair being slidable in diametrically opposite directions to engagebeneath diametrically oppostie parts of the protective housing. In sucha configuration, the resilient means biasing the detents outwardly maysimply comprise a resilient portion of each detent coacting with thediametrically opposed detent so that the two detents are mutually biasedapart.

The key-actuated release means is made surprisingly simple by shapingthe device to engage in a non-rotatable manner with the tape drive holeof the tape transport mechanism. Where such a release means requires aturning movement of a key for release of the device, the device is heldagainst rotation, while the key is being turned, by the tape lockingmechanism of the video-cassette. Commercially available video-cassetteshave inbuilt mechanisms to hold the tape transport reels againstrotation except when in use, and the above feature takes advantage ofthis to secure the device against rotation whilst the key is operatedfor releasing the locking means.

A variety of detent and release mechanisms may be used. However thepurpose of this invention is such that the device must be cheap and thatthere is no great need for absolute security as the cassettes can alwaysbe dismantled to extract the spool if serious theft is contemplated.

Thus preferably the device comprises a hollow cylindrical bottom shellportion which is received in use in one of the tape drive holes of thetape transport mechanism; a central spindle upstanding within the bottomshell portion; and a barrel within the bottom shell portion andpivotable about the spindle. Teeth upstanding from the barrel areengageable by a key placed around the spindle, and rotation of thebarrel effects retraction of the one or more detents to permit thedevice to be removed from the cassette.

Advantageously the teeth upstanding from the barrel have their openingfaces inclined at a low angle to their direction of movement so as tomake it difficult to rotate the barrel with a wire. Engagement of thekey with the faces of all teeth around the pin is needed before theresulting frictional force overcomes the tendency for the key to slideover the surface of the teeth. Such a construction would have aconsiderable resistance to attempts to remove the device using a pin,wire or sharp instrument.

Simplicity of construction and a smooth and functional outer shape canbe achieved if the device comprises a first moulding defining acylindrical bottom shell for fitting inside the video-cassette tapedrive hole, and an integral top plate for fitting flush with theprotective housing of the video cassette and closely cooperating withthe tapered edge of the hole surrounding the tape drive hole; one ormore second mouldings defining detent means slidably mounted in atransverse slot formed in the top plate portion of the first moulding; athird moulding comprising key-releasable locking means received insidethe bottom shell of the first moulding via a base opening therein forselective movement of the detend means; and a fourth moulding comprisinga base closure plate for the bottom shell of the first moulding. It isbelieved that this reduces the number of parts to a minimum, and becauseall such parts may be injection-moulded from thermoplastics material,use of non-magnetic or non-magnetizable metal materials can be easilyavoided.

The devices may be sold in packs of identical devices for use by aparticular person with a single key or identical keys.

Devices with different keys may be colour-coded or carry lockidentification letters or numbers to enable the members of the householdto distinguish the cassettes. The codings need not identify the matchingkeys in all particulars but merely identify them sufficiently to enablethe devices from one pack to be readily recognised even if the keyvaries from one pack to another.

DRAWINGS

In the drawings FIGS. 1 to 10 illustrate a first embodiment of a deviceaccording to this invention and FIGS. 11 to 16 illustrate a secondembodiment.

FIG. 1 is an axial section through a device according to this invention,in position in a video cassette where it blocks off one of the tapedrive holes of the tape transport mechanism. In FIG. 1 only a part ofthe video-cassette is shown, also in section;

FIG. 2 is a plan view from above of the device of FIG. 1, thevideo-cassette being omitted;

FIGS. 3 and 4 are side views of the device of FIG. 2, viewed in thedirections of arrows A and B respectively;

FIG. 5 is a schematic plan view similar to that of FIG. 2, but showingthe positions of certain internal parts of the locking means of thedevice;

FIGS. 6 and 7 are respectively axial sections through the device of FIG.5, taken in the planes X--X and Y--Y respectively;

FIG. 8 is an enlarged (for the purpose of clarity) section taken alongthe plane Z--Z of FIG. 6;

FIG. 9 is a projection elevation of the tooth layout of the barrel ofthe device, with the 180° of arc C-C' of FIG. 8 being laid out as alinear projection;

FIG. 10 is an axial section through the key needed to remove the deviceof the previous figures from a video-cassette housing;

FIG. 11 is an axial section through a second device according to thisinvention;

FIG. 12 is a plan view from above of the main body moulding of thedevice of FIG. 11;

FIG. 13 is a plan veiw from above of a unitary detent moulding of thedevice of FIG. 11, in which two detent portions are moulded in one piecewith resilient means biasing them mutually apart;

FIG. 14 is a perspective view of a barrel used as a detent actuatingmember in the device of FIG. 11;

FIG. 15 is a perspective veiw of a closure plate for closing a baseopening in a bottom shell of the main body moulding of the device ofFIG. 1 and for providing a journal spindle for the barrel of FIG. 14;and

FIG. 16 is a perspective veiw of a key for removing the device of FIG.11 from a tape drive hole of a video-cassette.

Referring first to FIG. 1 which shows the first embodiment of the deviceof the invention in position in a video-cassette, there can beidentified a tape transport mechanism 1 of the cassette in itsprotective housing 2. A leaf spring 3 biases the tape transportmechanism 1 upwardly as viewed, and the edge of the protective housing 2around the tape drive hole of the tape transport mechanism 1 is providedwith a downwardly and inwardly tapering edge 4 to assist location of thecassette accurately in a video recorder. All of this is common to anyvideo-cassette, whether of a BETAMAX or VHS type.

Inserted into the tape drive hole of the cassette of FIG. 1 is a device10 according to this invention. The device 10 fully blocks the tapedrive hole so that if the cassette is loaded into a cassette recorder,the automatic eject mechanism will fail to identify the cassette asbeing properly loaded, and the eject mechanism will automatically beactuated.

The device of the invention comprises five separate mouldings each ofthermoplastics material, which incorporate locking means which in thisembodiment engage beneath the underside of the protective housing so asto retain the device in the position shown in FIG. 1. The video-cassettecan be stored in its library case because the device is contained whollywithin the protective housing 2 and does not increase the effective bulkof the cassette. Moreover the device 10 can be removed only by the useof the key provided (as will later be explained) or by dismantling ordestruction of the cassette itself. The device therefore affords a veryeffective inhibition to casual mis-use of the video-cassette, at a lowcost and with a small number of separately moulded parts. Furthermorefrom the description below it will be seen that there are no metallicparts used at all, so that use of the device does not endanger thematerial recorder on the video tape by the introduction of magnetic ofmagnetizable materials into the zone of the tape.

Referring next to FIGS. 1 to 7 generally, it will be seen that thedevice 10 comprises a first moulded part 12 which comprises an annularportion 12a, a generally cylindrical boss portion 12b and an array ofaxial splines 12c around the boss portion 12b. The splines 12c areintended to mate with the internal splines of the tape drive hole of thetape transport mechanism of a conventional video-cassette.

From one to nine splines 12c may therefore be provided, although in theillustrated embodiment only three are shown (see in particular FIGS. 3and 4).

A second moulded part 13 comprises a top plate which is secured over theannular portion 12a of the first moulded part so as to leave radialchannels 14 therebetween as shown in FIG. 4. Detent members 15 areradially slidable in these channels 14, and as can best be seen in FIG.5 each detent member 15 comprises an identical moulding ofthermoplastics material so that the detent members 15 can be consideredas third moulded parts of the device. Each detent member 15 comprises atapered leading edge 15a for engagement beneath the protective housing 2of the video-cassette, and an integrally moulded resilient portion 15bwhich engages the trailing edge of the other detent member 15 of thepair, to bias the detent members radially outwardly in oppositedirections from the channel 14. A small hole 15c is moulded into eachdetent member 15, for engagement by pin means of a release barrel 16, aswill be described below.

It will be seen from FIG. 1 that the taper around the edge of the secondmoulded part 12 cooperates exactly with the tapered surface 4 of thehousing of the video-cassette, and that the annular portion 12a of thesecond moulded part and the protective housing 2 of the video-cassetteare of exactly the same thickness. The result is that the device 10 whenin position in the video-cassette lies exactly flush with the housing 2,with no cracks or openings around the edge of the device which mightenable an unauthorised user to insert a blade to try to prise or breakout the device.

Upstanding centrally from the base of the boss portion 12b of the firstmoulded part 12 is a central spindle 12d which is moulded integrallywith the remainder of the first moulded part. A single short spindle 12eis formed on the spindle 12d, near to its base. A fourth moulded partcomprises the release barrel 16 referred to above, which sits in thehollow interior of the boss portion 12b over the spindle 12d, and iscapable of a limited amount of rotation (approximately 90° ) untilfurther rotation is prevented by the spline 12e.

Integrally moulded with the release barrel 16 are two pin portions 16aeach of which is received in an appropriate one of the moulded holes 15cof the pair of detent members 15, so that rotation of the barrel isaccompanied by withdrawal of the detent members 15 into their radialchannel 14. Also integrally moulded with the release barrel 16 is anannular array of upstanding tapered teeth 16b arranged in a circleclosely around the central spindle 12d of the first moulded part. Theshape of these teeth will be understood from the comparison of theenlarged section of FIG. 8 and the projected tooth elevation of FIG. 9.The direction of movement of the release barrel 16 needed to effectwithdrawal of the detent members 15 is indicated by the arrow D in FIG.9, from which it will be seen that engagement of a key with the taperedsurfaces of the teeth, and not with vertical surfaces, is needed toeffect the necessary turning of the barrel 16. The angle of the taperedsurfaces can easily be designed such that only when a key is used thatcooperates with all or substantially of the tapered surfaces cansufficient frictional force be generated to effect the turning of thebarrel. Thus a fifth moulded part of the device 10 of the inventioncomprises a moulded key 17 as shown in FIG. 10 around the base of whichare moulded appropriate teeth 17a. In use the key is inserted over thespindle 12d until cut out portions 17b is received over the spline 12e.In this location, the teeth 17a of the key 17 mate closely with theupstanding projections 16b, permitting turning of the release barrel 16through an angle of 90° as permitted by the space E (FIG. 9) in the ringof upstanding projections 16b, into which space the short spline 12e islocated.

In use, the device simply has to be inserted in the central drive holeof either reel of the tape transport mechanism 1 of the video-cassette,and pushed axially downwards against the bias of the leaf spring 3 untilthe detent members 15 engage beneath the protective housing 2 of thecassette. Advantageously this engagement is achieved only on completecompression of the leaf spring 3 against the underside of the protectivehousing 2. This ensures that there is no free movement or slack in thelocation of the device, which might permit an unauthorised use to inserta knife blade or similar between the top plate 13 and the tapered wall 4of the protective housing 2.

Authorised removal of the device is permitted by insertion of the key 17over the spindle 12d, and turning through up to 90° while exerting adownwards pressure on the key to maintain good frictional contactbetween the teeth and the tapered surfaces of the projections 16b. Theleaf spring 3, which is the spool tensioning spring of thevideo-cassette, biases the device upwardly so that it can be removedfrom the video-cassette tape drive hole when the detent members 15 arefully retracted.

As so far described, the device of the invention can be inserted andlocked in any standard video-cassette without modification to either thedevice or the cassette. This is seen as a distinct advantage, althoughit is also contemplated that some manufacturers of video-cassettes mayprefer to modify the design of the cassette so that only the resultingmodified cassettes will accept a device according to the invention. Thisis readily achieved by shaping the base of each of the internallysplined tape drive holes of the tape transport mechanism 1 so that it isnon-planar. Corresponding shaping of the underside of the boss portion12b of the device of the invention ensures that only such a modifieddevice can be used with that particular video-cassette; otherwise thedevice cannot be pushed sufficiently deeply into the central hole of thetape transport mechanism 1 to achieve latching of the detent members 15beneath the protective housing 2.

Referring next to the embodiment of FIGS. 11 to 16, it will beappreciated that the operation of this second device according to theinvention is entriely analogous to that already described, although itsdetailed construction and manner of assembly differs. The secondembodiment comprises four injection-moulded parts. A first moulding 102(FIGS. 11 and 12) comprises a top plate 102a and an integral cylindricalboss portion 102b which together have the same shape and dimensions asthe first and second moulded parts 12 and 13 of FIG. 1. A principaldifference is that the boss portion 102b has an open base which isreferred to below, for insertion of a cylindrical barrel 104 analogousto the barrel 16 of FIG. 1.

Formed in the top plate 102a is a transverse guide channel 102c whichextends diametrically across the top plate 102a as shown in broken linesin FIG. 12. The channel 102c receives a detent moulding 112 which has apair of shaped detend edges 114 protruding in use from the recess asshown in FIG. 11. The detent edges 114 of the moulding 112 are joinedtogether by resilient webs 116 which in use bias the edges 114resiliently apart but which can flex to permit the edges to movemutually together in use as the device is inserted into or removed froma video-cassette tape drive hole.

Assembly of the device is achieved by first sliding the detent moulding112 laterally into the transverse guide channel 102c from one endthereof, then inserting the cylindrical barrel 104 into the boss portion102b from below, and finally pushing a closure plate 106 into positionto close the open base of the boss portion 102b. The closure plate 106is moulded with an integral stem portion 108 which acts as a journal forthe barrel 104 and ultimately for the key. The closure plate 106 isformed with a small peripheral flange 106a which is a snap fit in anundercut groove (not shown) of the boss portion 102b, to hold theassembly together.

The detent moulding 112 is formed with two small recesses 118 which isuse receive upstanding moulded pins 120 formed on the barrel 104.Turning of the barrel 104 through up to 90° causes the pins 120 to bearon the side walls of the recesses 118 to move the detent edges 114mutually together. The barrel 104 may be turned by means of a key 122which is injection moulded from thermoplastics material and whichcomprises a handle or gripping portion 124, a cylindrical stem 126 witha hollow centre 128 for receiving the stem portion 108 of the closureplate 106, and an annular array of spline recesses 130. The splinerecesses 130 of the key are made to mate with an asymmetric array ofinternal splines 110 moulded into the barrel 104, to match the key tothe barrel.

A lug 132 is moulded onto the key 122 as shown in FIG. 16, and in usecooperates with a quadrant-shaped cut-out portion of a key opening 102dformed in the top plate 102a, to limit the angular movement of the key.In this way it is ensured that the key 122 does not turn the barrel 104so far that the pins 120 escape from the recesses 118.

What is claimed is:
 1. A device for preventing unauthorised use of a video-cassette comprising a cassette, an internally splined tape drive hole of said video-cassette, blanking off said drive hole of the video-cassette to prevent unauthorised use of the cassette, characterised in that a blanking body (12) shaped to fit the tape drive hole in said video-cassette is provided with at least one detent (15) mounted to pass between the tape transport reel of the cassette, and an underside of a protective housing (2) of the cassette on compression of the spool tensioning spring by the tape transport reel; and key-release means (16) for effecting retraction of the said at least one detent (15) to permit removal of the blanking body (12).
 2. A device according to claim 1 in which the at least one detent (15) is biased radially outwardly into its locking postion by resilient means (15B) and is arranged to engage a bevelled annular edge (4) of the protective housing (2) of the cassette around the tape drive hole, to be cammed radially inwardly as the device is pushed into the tape drive hole.
 3. A device according to claim 1 further characterised in that the blanking body (12) and detent (15) are arranged so that the detent can just engage the housing underside with the spool tensioning spring substantailly fully depressed.
 4. A device according to any claim 1 or 2 or 3, further characterised in that the body (12) has means engaging between splines of the tape drive hole to prevent relative rotation therebetween, and the release mechanism (16) is a rotary mechanism, the blanking body (12) being held against rotation by the tape lock mechanism of the video-cassette.
 5. A device according to claim 4, further characterised in that the release mechanism (16) has surface configurations (16B) engageable by the key, comprising a spline or profile on a central annular portion of the barrel (16), around an axial spindle integral with the blanking body (12).
 6. A device according to claim 4, further characterised in that the release mechanism (16) surface configurations (16B) engageable by the key, comprising a plurality of annularly arranged teeth or holes on or in the bottom of the barrel (16).
 7. A device according to claim 6, further characterised in that the surface configurations are arranged so that a turning of the key (17) to release the device is only possible on applying as downward pressure on the key (17), onto the bottom of the barrel (16), to establish frictional contact with cooperating teeth thereon.
 8. A device according to any one of claims 1-3 and 9 or 10, further characterised in that the detents (15) are provided in one or more pairs, the detents of the or each pair being mutually biased apart and slidable in diametrically opposite directions to engage beneath diametrically opposite parts of the protective housing (2).
 9. A device according to claim 1, further characterised in that the blanking body comprises a first moulding (102) defining a cylindrical bottom shell (102b) for fitting inside the video-cassette tape drive hole, and an integral top plate (102a) for fitting flush with the protective housing of the video cassette and closely cooperating with the tapered edge of the hole surrounding the tape drive hole; one or more second mouldings (112) defining detent means slidably mounted in a transverse slot (102c) formed in the top plate portion (102a) of the first moulding (102); a third moulding (104) comprising key-releasable locking means received inside the bottom shell (102b) of the first moulding (102) via a base opening therein for selective movement of the detent means (112); and a fourth moulding comprising a base closure plate (106) for the bottom shell (102b) of the first moulding (102).
 10. A device according to claim 9, further characterised in that the key-releasable means received inside the bottom shell of the first moulding comprises one or more third mouldings (15) defining detent means slidably mounted between the first and second mouldings (12, 13) and a fourth moulding (16) comprising a member movable on key operation to coact with the detent means and move them to their retracted positions. 